Daniel Maler

Theta Pinch is one of the promising methods for the generation of hot and dense plasma. In this paper, we describe the results of experimental research on a small-scale Theta Pinch created with Helium or Hydrogen plasmas. Different plasma diagnostics, namely, optical, microwave cut-off, laser interferometry, visible spectroscopy, Thomson scattering, and Laser-Induced Fluorescence were used to characterize the time- and space-resolved evolution of the plasma parameters, and the specific features of these diagnostic results obtained are discussed. The measured plasma density and the electron and ion temperature evolution, obtained by these various diagnostic tools, agree to a satisfactory level. These methods will be applied for studies of the parameters of the plasma in the device that is being developed by the nT-Tao company towards fusion energy.

Theta Pinch is one of the promising methods for the generation of hot and dense plasma. In this paper we describe the results of experimental research on a small-scale Theta Pinch creating with Helium or Hydrogen plasmas. Different plasma diagnostics, namely, optical, microwave cut-off, laser interferometry, visible spectroscopy, Thomson scattering, and Laser Induced Fluorescence were used to characterize the time- and space-resolved evolution of the plasma parameters, and the specific features of these diagnostic results obtained are discussed. The measured plasma density and the electron and ion temperature evolution, obtained by these various diagnostic tools agree to a satisfactory level. These methods will be applied for studies of the parameters of the plasma in the device which is developing in Nt-Tao company towards the fusion energy.

Results of an experimental research and one-dimensional hydrodynamical simulations of critically damped sub-microsecond timescale underwater electrical explosions of wires made of 12 different materials are presented. Using current and voltage waveforms, streak shadow images of the shocks generated in water and wire expansion obtained by one-dimensional hydrodynamic simulations, the maximal values of the energy density, energy density deposition rates, and specific action integrals were determined. It is shown that for all study materials, the deposited energy density significantly exceeds the energy density required for the solid–liquid phase transition but is substantially smaller to induce a full liquid–vapor phase transition of the wire. At the time when the maximal value of the deposited power is realized, the deposited energy densities were found to be larger than the atomization energy for all materials. Estimates of the plasma parameters show that the explosion of the wires can be characterized by a high resistance and lowly ionized weakly coupled plasma. Three groups of materials were distinguished by either decrease, plateau, or increase in the resistance after the maximum of the deposited power. It was confirmed that the observed maximum Planckian temperature for all wire material does not exceed 6000 K due to the “bath” effect and that there is a correlation between the wire radial expansion and the strong shock wave velocities.

Pulsed-power-driven underwater electrical explosion of cylindrical or conical wire arrays produces supersonic water jets that emerge from a bath, propagating through the air above it. Interaction of these jets with solid targets may represent a new platform for attaining materials at high pressure (>1010 Pa) conditions in a university-scale laboratory. However, measurements of the internal structure of such jets and how they interact with targets are difficult optically due to large densities and density contrasts involved. We utilized multi-frame x-ray radiographic imaging capabilities of the ID19 beamline at the European Synchrotron Radiation Facility to explore the water jet and its interaction with a 50 μm thick copper foil placed a few mm from the surface of water. The jet was generated with a ∼130 kA-amplitude current pulse of ∼450 ns rise time applied to a conical wire array. X-ray imaging revealed a droplet-type structure of the jet with an average density of <400 kg/m3 propagating with a velocity of ∼1400 m/s. Measurements of deformation and subsequent perforation of the target by the jet suggested pressures at the jet–target interface of ∼5 × 109 Pa. The results were compared to hydrodynamic simulations for better understanding of the jet parameters and their interaction with the foil target. These results can be used in future research to optimize the platform, and extend it to larger jet velocities in the case of higher driving currents supplied to the wire array.

We present results exploring various methods of aluminum flyer acceleration. One method uses the shock wave generated by underwater electrical explosions of thin foils supplied by a pulse generator with stored energy of ∼4.7 kJ. Utilizing the shock created by an exploding foil, a maximal free flyer velocity of ∼2000 m/s is obtained. This acceleration method is compared to results exploiting only magnetic pushing to accelerate flyers using a common strip-line configuration, resulting in much lower velocities of ∼300 m/s. We also present a modified strip-line configuration, for which a significant increase in the flyer velocity to ∼1200 m/s is measured. Finally, a hybrid strip configuration, incorporating both the effects of magnetic pushing and acceleration by exploding foil and its subsequent shock wave, results in ∼1400 m/s flyer velocity. These experimental results are analyzed by numerical simulations and analytical modeling of the conservation equations of mass and momentum.

We present results on underwater electrical explosions of thin aluminum and copper foils using a generator delivering ∼200 kA current amplitude, ∼0.9 μs rise time pulses. Time-resolved shadow imaging displays the generation of a strong planar shock wave in water in the vicinity of the exploding foil. Using time-resolved spectroscopy, aluminum oxide (AlO) absorption bands were observed in a Planckian-like spectrum, indicating that aluminum combustion starts when aluminum vaporizes. It is also shown that the strongest shock wave is obtained for the largest linear energy deposition rate to the foil.

Experimental and magnetohydrodynamic numerical simulation results and analysis of a μs- and sub-μs-timescale overdamped underwater electrical explosion of copper wires having different lengths and diameters are presented. For these explosions, ∼80% of the energy stored in the pulse generator is deposited into the wire during a time comparable or shorter than a quarter period of the underdamped discharge. It was found that the threshold values of the deposited energy density, energy density rate, and energy density per unit area, which satisfy overdamped discharge, depend on the wire parameters and on the timescale of the explosion. It was shown that the mechanism responsible for this is the process during which the wire experiences phase transitions to a low-ionized plasma, the resistivity of which is determined by the electron–neutral collision rate, which, in turn, depends on the wire radial expansion velocity, current density, and temperature.

New analytical solution of the piston and shock evolution for the wire electrical explosion in water is obtained. This is provided on the base of the compressible Euler equations without usually a prior introduction of any self-similarity hypothesis. It is shown that diverging cylindrical shock is transformed into acoustic wave in a finite time, even without taking into account of dissipation. The correspondence with experimental data on underwater electrical explosion of thin wire is represented.